Well I went by Fry's today and got to see both the 732 and 831, although not side-by-side where I could do a really thorough comparison (plus it was 65831 vs 57732). Bottom line for me was that I couldn't see enough difference to justify the price jump; maybe with more time and the ability to do a side-by-side comparison I would have seen more of a difference. But the 732 looked great despite being at the edge of the TV area where it was under regular in-store lighting, as opposed to the darkened area that the 831 was in. Right next to the 57732 was the Samsung 1080p Pedestal set and there was no comparison, the 57732 was better especially in the blacks. The 732 is most definitely improved over the 731 in this aspect.
So, my 57732 will be delivered on Monday, I can't wait. BTW another factor to consider, based on the stores I've visited dealers are much more willing to discount the 732 than they are the 831 at this point, so to me that makes the value proposition of the 732 that much better.